You use Jagannatha Hora software. Inventor of JHora is Pt.Sanjay Rath's student with input from Teacher itself
You have to go by talented and knowledgeable traditional astrologer cum teacher guidance on Chara Karakas, therefore you have to consider Rahu

Dasa of Chara dasa to be utilized is Sage's calculation system. If at all you want to try you can use Rangacharya, and third one You can very well ignore.

It is upto you.. the point is one should get output..
i use 7 and got good results while using chara dasa

but now while reading Narayan dasa by Sanjay Rath, we need to used 8 charakaraks..
Also there is difference in use of exceptions while calculating arudha pada.. i think it is better not to use exception while using 7 charakarakas..